Uptake of extracellular Ca²⁺ and not recruitment from internal stores is essential for T lymphocyte proliferation

Abstract

Changes in free cytosolic calcium concentrations ([Ca2+]i) are thought to be important initiating events in the activation of T lymphocytes. Mitogen-induced increases in [Ca2+]i may result from net influx across the plasma membrane and/or release of Ca2+ from intracellular stores. In human T lymphocytes loaded with the fluorescent indicator indo-1, addition of phytohemagglutinin (PHA) or the anti-CD3 antibody UCHT-1 elicits a biphasic [Ca2+]i response. A major component of the initial transient peak was due to release from internal stores whereas the lower plateau phase was sustained by Ca2+ influx. Previous work suggested that Ca2+ influx is essential for interleukin 2 (IL 2) secretion and cell proliferation. To determine the relative effects of the initial and sustained phases of [Ca2+]i change, IL 2 secretion and cell proliferation, we introduced into the cell 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a high affinity intracellular Ca2+ chelator which neither contributes to nor interferes with the fluorescence determinations of [Ca2+]i. In cells preloaded with BAPTA, both PHA and UCHT-1 antibody failed to elicit the transient [Ca2+]i overshoot. Only the plateau phase could be observed in the presence of extracellular Ca2+. In contrast, BAPTA-loaded cells were found to be fully functional when assessed for IL 2 receptor expression, IL 2 secretion and cell proliferation. Thus, the mitogen-induced, maximal but transient increase in [Ca2+]i, contributed to mainly by release of Ca2+ from internal stores, does not appear to be essential for these T cell responses.

Characterization of altered calcium signalling in T lymphocytes from patients with rheumatoid arthritis (RA)

“…1), but it is not possible to comment fully on the release of Ca 2 from endoplasmic reticulum stores. Initial reports on the rise in T cell Ca 2 after stimulation had suggested that the initial peak seen was mainly due to release of Ca 2 from intracellular stores [28]. Our own observations, and those of other groups [35][36][37], demonstrate that this store of Ca 2 contributes only a small fraction to the initial Ca 2 elevation.…”

“…The control cells gave the typical response observed by many groups [28][29][30], of an initial rapid increase in cytoplasmic calcium after a delay of 20-30 s from the addition of the stimulus. The rapid increase occurred over a period of about 30 s and was followed by a decline to an equilibrium calcium concentration, which was then sustained for the period of observation (Fig.…”

Calcium dependence of T cell proliferation following focal stimulation

“…This could, for instance, be the case in SCID patients carrying the ORAI1 mutation [13,14] [Ca 2+ ] i values at these time points, we cannot, however, imagine that these two time points do not reflect the general behavior over the 2 days. The initial high [Ca 2+ ] i , which is mostly due to Ca 2+ release is not sufficient to drive gene expression and cell proliferation [35]. This has been shown several times and recently most dramatically in some SCID patients with CRAC mutations [13,14].…”

A p56 -independent Pathway of CD2 Signaling Involves Jun Kinase

“…In p56 lck expressing T cells, TCR stimulation is followed by an initial high transient Ca 2ϩ peak and a lower amplitude but sustained plateau phase (41,44,46). The initial rise of Ca 2ϩ is caused by the inositol trisphosphate-mediated release of Ca 2ϩ from the endoplasmatic reticulum (45) but is not sufficient for proliferation or IL-2 gene expression (41,71). Rather the prolonged elevation of intracellular Ca 2ϩ due to the Ca 2ϩ influx from extracellular sources is the critical component of the Ca 2ϩ signal (41,71).…”